2 Why We Need Model-Based Testing

246 Compositional Modeling
For parameter generation one can also use dependent features of model programs
if parameter selection is most conveniently done by reading the state of the contract
model program.
14.4.4 Property checking
One can write a model program to describe a temporal property that describes a “bad”
behavior of the contract. For example, a certain pattern of actions leads to a state
where a safety condition in the property model program is violated. Composition of
the contract model program with the property model program can be explored for
safety analysis (as we demonstrated in Chapter 7, Section 7.5).
One can also write a state-dependent condition in a separate feature that reads
state variables of multiple features and defines a global safety condition spanning
those features. It is asssumed here that the feature model programs use distinct state
variables, so the safety condition is not specific to any single feature model program.
14.4.5 State refinement
One can use composition to abstract details of subbehaviors. The idea is the following.
Suppose you have a model program A that includes two actions StartB() and
FinishB(). There is another model program B that describes the behavior of B. The
only action symbols that A and B have in common are StartB() and FinishB(). When
A is explored in isolation, then StartB() leads to a state "B-Is-Working" where the
only enabled action is FinishB(). The only action that is initially enabled in B is
StartB() and the last action of B is FinishB(). A composition of A and B provides
a refinement of the state "B-Is-Working" where all the behavior of B is included.
14.5 Exercises
1. Finish the model program M for M1 × M2 that was started in Section 14.3.1 for
all actions. Use mpv to convince yourself that the traces of M are the same as the
traces of M1 × M2.
2. Extend the previous exercise to include also the credits model program and the
commands model program.
3. Write a model program M with two features F1 and F2 such that F1 and F2 share
state variables and use the same actions A and B, and the set of traces of M is
not an intersection of the set of traces of M restricted to F1 and the set of traces
of M restricted to F2.Usempv to check the result.
4. Write a utility that given a regular expression over actions (possibly including
placeholders) generates the corresponding FSM.
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